Coded excitation with lead-free ultrasonic arrays : from complex structural integrity assessments to intravascular ultrasound imaging

Germano, Elmergue

Thesis

Coded excitation with lead-free ultrasonic arrays : from complex structural integrity assessments to intravascular ultrasound imaging

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Creator

Germano, Elmergue

Rights statement

Strathclyde Thesis Copyright

Awarding institution

University of Strathclyde

Date of award

2026

Thesis identifier

T17601

Person Identifier (Local)

202170109

Qualification Level

Doctoral (Postgraduate)

Qualification Name

Doctor of Philosophy (PhD)

Department, School or Faculty

Department of Electronic and Electrical Engineering

Abstract

The superior piezoelectric coefficients of ceramics, including Lead Magnesium Niobate-Lead Titanate (PMN-PT) and Lead Zirconate Titanate (PZT), make them ideal for high performance transducers, driving their extensive use in industrial and medical sectors. However, the presence of lead in these materials has raised apprehensions about potential risks to the environment and human health. To comply with global regulations, the prompt adoption of lead-free alternatives is essential to advance the development of environmentally sustainable piezoelectric materials. In Non-Destructive Testing (NDT) contexts, the growing complexity of components has driven the development of flexible ultrasonic probes, allowing efficient inspection without requiring custom wedges to accommodate to intricate surfaces. In medical settings, piezoelectric transducers such as those based on PMN-PT are the preferred choice for commercial Intravascular Ultrasound (IVUS) catheters owing to their mature fabrication processes. Nonetheless, the lead content in these materials raises health and safety concerns, and this work explores the application of scalable, lead-free, flexible, high frequency (~20 MHz) ultrasonic arrays in these two settings. Coded excitation strategies in conjunction with Full Matrix Capture (FMC) and Total Focusing Method (TFM) were applied to inspect thick non-planar industrial components. The Golay-based TFM demonstrated superior performance compared to the pulse-based TFM. Golay excitation strategies offer reduced data acquisition and frame rate (by a factor of two) compared to single transmission excitations, and can introduce motion-dependent decoding errors. Therefore, investigations on single transmission Barker and chirp signals were also undertaken. Moreover, a novel Signal-to-Noise Ratio (SNR) approach was introduced, enabling the evaluation of a single-cycle pulse, Barker and chirp excitation schemes in simulation and experimentation. The ultrasonic array demonstrated excellent conformity to the non-planar components, and the coded excitation schemes consistently achieved better imaging quality in relation to pulse excitation. The medical context introduced a scalable, RoHS-compliant, 5 French gauge ultrasonic array, leveraging its fabrication benefits for IVUS imaging. Despite exhibiting lower piezoelectric coefficient values in relation to its lead-based counterparts, resulting in reduced signal quality, the lead-free array demonstrates effective imaging performance through the use of coded excitation strategies, enabling the detection of calcified plaques in ex-vivo porcine heart arteries. The array was then characterised through electrical impedance and pulse echo responses. Coded chirp and Barker excitations were used to image the arteries, detecting calcified plaques, with chirp offering better imaging quality. A 10-μm haematoxylin and eosin histological section of an artery was used for comparison with an IVUS image, showing strong concordance in detecting the calcified plaque. The accumulation of this work underscores the potential of flexible lead-free RHS-compliant arrays as an effective approach to address the increasing complexity of industrial components and a sustainable solution for the next generation of IVUS systems. Combining the array with coded excitation provides additional SNR gain and increases penetration depth, which enhances the scope of industrial and medical applications to which this flexible lead-free array can be deployed.

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